Patient Controlled Analgesia (PCA) is a method for delivering parenteral narcotics wherein a patient controls the administration of the narcotic analgesics, since the patient is usually in the best position to determine the need for additional pain control. PCA is commonly administered via a stand-alone type of infusion device dedicated solely for PCA use. Examples of PCA devices are disclosed in U.S. Pat. No. 5,069,668, to Boydman, and U.S. Pat. No. 5,232,448, to Zdeb.
The primary serious side effect of narcotic analgesics in the medical practice is central nervous system and respiratory depression which can result in serious brain damage or even death. However, PCA is a relatively safe means for administering narcotic analgesics, at least in theory, because if the patient self administers too much analgesic, the patient usually becomes drowsy and falls asleep. Thus, for the majority of the patients, PCA is a safe and effective means for pain control. Nonetheless, there have been cases of respiratory and central nervous system depression and even death associated with the administration of PCA. The causes include clinical errors in programming the PCA device, errors in mixing or labeling analgesics, device malfunction, and even overzealous relatives who administer extra doses of analgesics by pressing the dose request cord for the patient.
Despite the potential dangers of narcotic analgesic overdose, narcotic antagonists such as naloxone (Narcan) are widely available and commonly used in hospitals for reversal of respiratory and central nervous system depression. However, the effectiveness of such narcotic antagonists is highly dependent on prompt recognition and treatment of respiratory and central nervous system depression, as such depression can cause brain damage or even death due to lack of oxygen. Thus, respiratory and central nervous system depression must be recognized and treated promptly to assure a higher probability of successful recovery.
For detection of potential respiratory depression associated with the administration of narcotic analgesics, a system which indicates a patient's respiratory and cardiac status without the need to invasively measure or sample the patient's blood is particularly desirable and useful. Non-invasive pulse oximetry is one such method to monitor the oxygen saturation of a patient's blood and the patient's pulse rate. The combination of the blood oxygen saturation and pulse rate can be an important indicator of overall patient respiratory and cardiac status.
One common approach to non-invasive pulse oximetry uses a dual-wavelength sensor placed across a section of veinous tissue such as the patient's digit to measure the percentage of hemoglobin oxygenated in the arterial blood, and thereby measures the patient's oxygen saturation level. In addition, since the oxygenated hemoglobin at a specific tissue position is pulsatile in nature and synchronous with the overall circulatory system, the system indirectly measures the patient's pulse rate. Examples of similar pulse-oximetry sensors are disclosed in U.S. Pat. No. 5,437,275, to Amundsen et al., and U.S. Pat. No. 5,431,159, to Baker et al.
Patient care systems providing for central control of multiple pump units, potentially including PCA units, are known in the medical field. Examples of such systems are disclosed in U.S. Pat. No. 4,756,706 to Kerns et al., U.S. Pat. No. 4,898,578, to Rubalcabe, Jr., and U.S. Pat. No. 5,256,157, to Samiotes et al. Each of these prior art systems generally provides a controller which interfaces with a plurality of individual pumps to provide various control functions. An improved patient care system is disclosed in U.S. patent application Ser. No. 08/403,503 (U.S. Pat. No. 5,713,856) of Eggers et al. The central management unit of the Eggers et al. system can, for example, obtain infusion parameters for a particular infusion unit from the clinician and serve as an interface to establish the infusion rate and control infusion accordingly, individually control the internal setup and programming of each functional unit, and receive and display information from each functional unit. The Eggers et al. patient care system also provides for central control of various monitoring apparatus, such as pulse oximeters and heart monitors.
However, systems described above which are capable of controlling PCA and a pulse oximeter do not provide integrated control of the PCA device in conjunction with the pulse oximeter.
Such systems would require constant dedicated monitoring by medical personnel in order for prompt detection and treatment of potential respiratory depression side effect associated with the administration of narcotic analgesics. Thus, these systems are not cost-effective because of the added expense from constant monitoring by medical personnel.
Furthermore, the systems discussed above do not automatically shut-off of the PCA unit in the event of respiratory depression. Without automatic PCA shut-off, these systems actually allow further administration of the narcotic analgesics which can further aggravate the respiratory depression until appropriate medical personnel arrives to intervene. The time for medical personnel to arrive and intervene will delay administration of narcotic antagonists and thereby potentially compromise their effectiveness.
Because of disadvantages associated with existing PCA systems, certain patients who might otherwise benefit from the PCA method of therapy may not be PCA candidates because of concerns about respiratory depression. Even if a patient were eligible for PCA treatment with prior art systems, these systems do not allow the patient to receive a more aggressive treatment because of the risk of inadvertent respiratory depression and thus the patient would not be able to obtain quicker and more effective pain relief from a more aggressive treatment.